What is ISDN? As a short word, some network engineers use ISDN network terminology for WAN connection using ISDN technology. ISDN stands for Integrated Services Digital Network which provides switched (dialed) digital WAN services in increment of 64 Kbps.
ISDN Network availability is widespread, but you can still find places where it is simply not available. One key reason to use dialed connections of any kind, including ISDN network, might be to send and receive data for only short periods of time. Routers frequently use ISDN network to create a backup link when their primary leased line or Frame Relay connection is lost. ISDN technology uses T-carrier technology to quickly and efficiently send digital data streams over existing phone lines.
ISDN network Channel
ISDN network includes two types of interfaces: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). Both BRI and PRI in ISDN technology provide multiple digital bearer channels (B channels), over which temporary connections can be made and data can be sent. Because both BRI and PRI have multiple B channels, a single BRI or PRI line can have concurrent digital dial circuits to multiple sites, or multiple circuits to the same remote router to increase available bandwidth to that site.
In ISDN technology, B channels are used to transport data. B channels operate at speeds of up to 64 kbps. ISDN network signals new data calls using the D channel. When a router creates a B channel call to another device using a BRI or PRI, it sends the phone number it wants to connect to inside a message sent across the D channel. The phone company’s switch receives the message and sets up the circuit. Signaling a new call over the D channel is effectively the same thing as picking up the phone and dialing a number to create a voice call.
The different types of ISDN network lines are often described with a phrase that implies the number of each type of channel. For instance, BRIs are referred to as 2B+D, meaning two B channels and one D channel. PRIs based on T1 framing, as in the U.S., are referred to as 23B+D, and PRIs based on E1 framing are referred to as 30B+D.
Dial-on-demand routing (DDR)
ISDN technology is commonly used in dial-on demand routing; a router with a temporary, dial-up link can simulate a permanent WAN link. When there is no more data to send, or if the line has been inactive for a certain period of time, the router closes the link. Dial-on demand routing in ISDN network reduces the amount of time a line is in use, thereby reducing connection charges. In addition, dial-up WAN solutions typically cost less than always-on WAN connections. You can use DDR if your WAN traffic is periodic rather than constant.
ISDN network specifications are controlled by the International Telecommunications Unions Standardization Sector (ITU-T).
ISDN network - OSI model
How ISDN network and the OSI model relate?
ISDN technology consists of lower layers of physical and data link and Network layers standards of the OSI model. ISDN network uses PPP or LAPD for data encapsulation method at the Data link layer. It uses the detail of this layer for link establishment; administration; and error control.
ISDN standards
ISDN standards are grouped according to function. The protocol grouping and descriptions follows a lettering standard.
- ISDN E standard: standards for ISDN network on the existing phone network, such as international addressing
- ISDN I Standard: standards for ISDN network concepts, terminology, and services, such as network services
- ISDN Q standards: standards for switching and signaling, such as call setup, flow control, and error correction
ISDN network is a relatively inexpensive WAN solution when compared with other WAN options. The diagram below is an ISDN network connection.
When the use of ISDN network is required, follow the guidelines recommendation below:
- ISDN network is suitable standard offering connections up to 128 Kbps using BRI (basic rate interface) and up to 2.048 Mbps using PRI (Primary rate interface).
- For new router configuration using ISDN network:
- Terminal adapters (TAs) must not be used.
- Routers with native ISDN BRI or PRI ports must be used
- PPP encapsulation must be used on temporary dial-up links that require authentication. SLIP connections must be avoided.
- PPP PAP or preferably CHAP must be used to secure ISDN PPP dial connections
- For new router configurations using ISDN technology with PPP, CHAP must be used for increased authentication security.
Remote clients / tele-workers that need to connect to the corporate network should use high degree security connection using the VPN tunneling. The remote clients should be a clean computer with proper security protection such as using internet security software BitDefender.
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